1. Field of the Invention
This invention relates to hulls for watercraft, and more particularly to a low-drag, high-speed displacement-type hull having a constant-section midbody extending over at least one-third of its waterline length.
2. Prior Art
The development of high-speed displacement-type watercraft hulls has been virtually stagnating for the past half-century, mainly because of the obstacles, heretofore believed insurmountable, presented by the rapid increase in the wave-generating drag attendant with increased speed. Improved analytical and model testing techniques have led to minor advances in the definition of the optimum hull, but the bulk of the effort devoted to the increase in the economically attainable limiting speed has been concentrated on planing hulls, hydrofoils and other hull forms which depend on dynamic lift generation, rather than displacement craft.
Problems of stability, construction cost, the need for operating in a displacement mode until sufficient forward velocity is achieved for the lift mechanism to become effective have generally limited the application of planing and hydrofoil hulls to relatively small vessels such as small naval craft, short-range ferryboats and pleasure craft, for which cost and operating economics are of secondary consideration.
Some improvements in the cruising speeds of commercial load-carrying vessels have been obtained by the steady increase in the size of their hulls, with the attendant reduction in the Froude Number for a given absolute velocity, and by the introduction of bulbous submerged forebodies designed to generate an out-of-phase wave train at certain specific speeds to interfere with the wave generation of the hull proper. Presently these techniques are applied to large ships operating at low Froude numbers and having hulls of otherwise conventional shape.
The primary object of this invention is to provide for the construction of displacement hulls having greatly reduced wavemaking resistance and surface friction.
Another object of the invention is to teach the design of such hulls which are simple in form and readily constructed with conventional techniques and materials.
A further object of the invention is to teach the design of a high-speed displacement hull in which a substantial portion of length comprises a parallel midbody of constant and full section.
Another object is to teach the design and construction of multi-hulled vessels with small hull spacing factors, employing hulls having the characteristics defined above.
Yet another object is to provide a class of displacement craft employing hull forms in the range of Froude numbers between 0.60 and 1.20, which require appreciably less propulsive effort than that required by equivalent conventional hull forms.